The present invention pertains to a system for facilitating an order change in the dry end conversion of a corrugated paperboard web. In particular, the invention relates to a method for maintaining web continuity on both levels of a double level dry end.
In a corrugator dry end, where a corrugated paperboard web is longitudinally scored and slit into multiple parallel output webs (or “outs”), the outs are directed through one or more downstream cutoff knives which cut the output webs into selected sheet lengths. When two cutoff knives are used, they are vertically separated and each is capable of cutting the full corrugator width web. A web selector positioned downstream of the slitter/scorer, divides the outs into two groups, one of which is directed to the upper cutoff knife and the other to the lower cutoff knife. Order changes must be effected while the upstream corrugated web end continues to produce and deliver the continuous web to the sitter/scorer. An order change will typically result in a change in widths of the output webs, requiring redirection of at least a central portion of the web from one knife level to the other and possibly changes in edge trim widths as well.
The prior art has developed two basic order change systems for corrugator dry ends utilizing double level cutoff knives. One system is known as a gapless or plunge style order change system. In this system, there are two slitter-sorer stations immediately adjacent one another in the direction of web movement and through both of which the web travels. At order change, one slitter/scorer, operating on the currently running order, will lift out of operative engagement with the web, and the other slitter/scorer which is set to the new order alignment plunges down into operative engagement with the web. The result is a small order change region of corrugated web with overlapping slits and scores for both the running and the new orders.
FIGS. 1-3 show different ways of sorting out the abutting slit lines to implement the order change. FIG. 1 shows a prior art order change according to European Patent 0 458 340 A2 involving an expiring (running) order with three slit webs U1 going to the upper level of a cutoff knife and one slit web L1 going to the lower level of the cutoff knife. The new order will have a single web U2 going to the upper level and two slit webs L2 going to the lower level. The order change is implemented by lateral cut N0 made in the center of the web connecting the innermost slit S14 between upper and lower level webs on the old order to the innermost slit S22 between upper and lower levels webs on the new order. This allows web selectors to reset as the running order passes.
This order change strategy has at least two significant problems. First, it is very difficult in practice to have the tools creating the slit lines plunge into and out of the web abruptly at contact with lateral cut line N0. Additionally, when the level transitioning from wide to narrow has outs narrower in width than the distance between the innermost slit line S14 on the running order and the innermost slit line S22 on the new order, one or more of the outs going to that level will be totally severed. This totally severed out can accelerate faster than its mating outs due to a slipping knife infeed pull roll. The totally severed out will then buckle and frequently jam in the knife.
FIG. 2 shows a different strategy for implementing the order changeover as disclosed in U.S. Pat. No. 5,496,431. This strategy involves creating an order change region that is formed between the front end of the new order sheets and the rear end of the running order sheets and creating a transitional slantwise slit, running at a predetermined angle with respect to the running direction of the continuous web, connecting the innermost slit between the upper and lower level webs in the running order to the innermost slit between the upper and lower level webs in the new order.
This order change method creates end of order waste that is of a different width and length from the expiring order outs. In addition, the pieces that are created when the waste goes through the cutoff knife may be small and angular shaped, creating potential for jam-up in the knife or at exit of the knife.
Yet another order change strategy, shown in FIG. 3, is disclosed in U.S. Pat. No. 6,092,452. With this strategy, an order change zone is created by lifting the slitting tools of the running order from the board line prior to plunging the tools of the new order into the board line. The concept then involves delaying the lift-up of one slitting tool associated with the innermost slit between the upper and lower levels of the running order and bringing forward the slitting tools associated with the innermost slit between the upper and lower knife levels of the new order into the order change zone. The effect of this is to create an overlap in the innermost slits on the running and new orders in the order change zone so that these slit lines can be connected by a lateral slit that may be perpendicular to the direction of forward travel of the web.
This order change method allows the connection of the slit lines defining the old and new orders with no severing of some of the outs going to the level with transition from wide to narrow outs. It avoids the problem of diagonal scrap pieces, but it also creates order change waste that is problematic. FIG. 4 shows waste removed from a stacker that was created on the upper and lower levels with this order change strategy. The waste is wider and longer than the sheets being discharged at the tail of the old order. As a consequence, the waste must be removed from the stacker transport conveyor prior to its entrance to the stacker or it will jam at the stacker bay. This is difficult for the stacker operator to accomplish and constitutes a large amount of waste sheet.